The screen turns into a color (mostly grey or black but can also be blue or white with black strips) and stays like this you can't do anything, if there was sound, there is no sound anymore. I also noticed that if I leave it like this a bit the fans slow down and the computer is more quiet like if it idles. the only way to fix it is to force a restart by long pressing the power button and if this does not work by plug out/in the power supply.